The present invention relates to heavy-ion therapy systems for the treatment of cancer and the like, and in particular to a treatment planning tool for generating settings for particular dose profiles for heavy-ion beams.
External beam radiation therapy may treat a tumor within a patient by directing high-energy radiation in one or more beams toward the tumor. The radiation commonly may be photons, such as x-rays or electrons.
Standard electron beam and photon devices are often used to provide single energy beams during treatment. More complex dose patterns can be obtained, however, with combinations of beams of multiple radiation energy. U.S. Pat. No. 7,202,486 to Gentry et al. issued Apr. 10, 2007, entitled: Treatment Planning Tool For Multi-Energy Electron Beam Radiotherapy, assigned to the same assignee as the present invention and hereby incorporated by reference, describes a tool allowing a physician to combine multiple electron beam energies or combined electron/photon energies available on a standard, single beam radiotherapy system. The tool, which may operate on a stand-alone desktop computer, accepts a simple characterization of a desired beam depth dose profile and produces a treatment plan using multiple energies and that can be entered into a radiation therapy treatment planning system and implemented using successive exposures from the radiation therapy machine. The use of multiple energy beams allows for better dose conformance to a treatment zone.
Recent interest has developed in the use of protons or other heavy-ions for external beam therapy. Unlike electrons and x-rays, protons may be given sufficient energy to penetrate an arbitrary amount of tissue and then to stop within the tissue, eliminating exit dose through healthy tissue on the far side of a tumor. Further, the dose deposited by a proton beam is not uniform along the entrance path of the beam, but rises substantially at a “Bragg peak” near a point where a proton stops within the tissue. These two features allow improved concentration of dose within the tumor.
A mono-energetic beam of protons produces a narrow Bragg peak whose range (depth in the tissue) can be controlled by controlling the energy or acceleration of the protons. In theory, an arbitrary dose profile can be produced using a mono-energetic beam of protons by moving the beam in energy range and angle to dimensions to sequentially “paint” a treatment zone. By changing a dwell time of the proton beam at a particular location, an arbitrary dose profile may be produced.
Current proton therapy may alternatively use a “spread out Bragg peak” (SOBP) employing a poly-energetic proton beam having multiple Bragg peaks extending over a range of depths to produce a plateau of roughly constant dose. This approach accommodates poly-energetic proton sources and greatly simplifies the mechanics of treatment by allowing an entire tumor area, embraced by the plateau, to be treated simultaneously without complex movement of the beam.
Producing a spread out Bragg peak may be done, for example, by passing a mono-energetic or narrow poly-energetic beam of protons through a rotating wedge “propeller” that modulates the energy of the proton beam with constantly changing variable thickness of material or through a grid having varying thicknesses within the cross-section of the beam. The overall energy of the beam, and hence the center of the plateau may be adjusted in range or depth by using a bolus or movable wedge to center the spread out Bragg peak at the tumor.
Treatment planning using an SOBP beam simply requires adjusting the width of the plateau of the SOBP to cover the tumor and centering the range of the plateau on the tumor, and then applying the proton beam for a desired period of time to achieve a uniform tumor dose.